Patent No. DE 10 2008 054 645 A1 discloses a tank for a service liquid in a motor vehicle wherein the tank is used for providing an aqueous urea solution in a motor vehicle.
One problem with respect to providing an aqueous urea solution that is used as a reducing agent for reducing nitric oxides in the exhaust gas stream of internal combustion engines is its comparatively high freezing point. It freezes as early as at temperatures of −11° C. and below, which are easily reached during winter periods in central Europe.
When aqueous urea solution freezes, it expands to a substantial extent, which can cause a substantial mechanical load on the tank storing the urea solution. In the course of this, when freezing, the aqueous urea solution may expand to such extent that the tank bursts. This problem is aggravated even further if during the freezing of the aqueous urea solution in the tank, a liquid bubble completely enclosed by already frozen solution forms, which freezes last. As a result of the freezing of a liquid bubble that is enclosed by an already frozen solution, enormous forces may occur on the freezing solution and thus on the tank wall regions wetted thereby.
The known generic document therefore teaches insulation elements that are locally disposed on the outside of the tank, in order to prevent locally any thermal passage from the inside of the tank to the outer environment of the tank and to ensure in this way a directed ice formation in the tank.
The generic document further teaches to provide the insulation elements above all in places where sensitive units are provided in the tank, for example sensors or conveying devices and the like, in order to prevent the destruction thereof during freezing of the solution.
What is of disadvantage in the known generic solution is the associated high manufacturing and assembly complexity, since first of all, insulation elements have to be produced for a service liquid tank, which must allow a gap-free mounting to the tank so as to allow their thermal insulating effect to develop to its full potential. Moreover, these insulation elements, which have to be manufactured with a high degree of accuracy, have to be separately mounted after the assembly of the tank.